1. Field of the Invention
The present invention relates to a design support system utilizing an information processor for supporting a design of a printed board, and a method of supporting a design of a printed board, as well as a design support program to be implemented by the design support system. The present invention more particularly relates to a design support system for supporting a design of a printed board for suppressing electromagnetic interference from a printed board, and a method of supporting a design of a printed board for suppressing electromagnetic interference from a printed board, as well as a design support program to be implemented by the design support system for suppressing electromagnetic interference from a printed board.
2. Description of the Related Art
Undesired electromagnetic wave radiated or emitted from electric, electronic or electron devices may cause electromagnetic interference. The electromagnetic interference may be influential to any broadcastings and any communications. Various national regulations to the electromagnetic interference have been established in various countries. Some international regulations have also been established. CISPR international regulation is a typical one of the existent international regulations.
A frequency band, which is at present subject to the regulation, is ranged from 30 MHz through 1 GHz. It is necessary for manufacturing companies to suppress the electromagnetic interference of their products into a regulatory acceptable range. A measurement of the electromagnetic interference of the final products is made in accordance with the regulation. The measurement is thus made after the final products have been completed, and is sometimes made just before shipping of the final products. In case, just before shipping of the final products, it can be confirmed that the final products do not satisfy the regulations for the electromagnetic interference. A prompt counter-measurement thereto is needed, wherein additional parts may be placed to the products or a redesign of the products or a modification to the products may be made alternatively. These counter-measurements may cause some delay in shipping the final products allowable in the regulations for the electromagnetic interference, or some increase in the manufacturing costs.
Another method for solving the above problems was proposed, wherein a system and a method of designing a printed board adopted to suppress the electromagnetic interference. The printed board is the main factor for causing the electromagnetic interference. The other design support system for the printed board has an additional design function for suppressing the electromagnetic interference. Japanese laid-open patent application No. 10-49568 discloses a circuit board design method and a storage medium. Japanese laid-open patent application No. 10-91663 also discloses a printed board computer-aided design system.
FIG. 1 is a flow chart of respective steps involved in a conventional layout method for the printed board disclosed in Japanese laid-open patent application No. 10-49568. It is considered that the electromagnetic interference caused by electromagnetic wave emitted from signal lines on the printed board is dominant for the electromagnetic interference problem with the printed board. In this viewpoint, a quantity of radiation of the electromagnetic wave causing the electromagnetic interference from the signal lines is estimated or calculated. If the calculated quantity of radiation exceeds the upper limit, then any counter-measure is made and an optimum layout for realizing the counter-measure is also decided.
FIG. 2 is a schematic view explaining operations of the conventional printed board CAD system disclosed in Japanese laid-open patent application No. 10-91663. If a wiring is designated on the CAD system, then a quantity of radiation of the electromagnetic wave causing the electromagnetic interference from the designated wiring is calculated by the CAD system based on given information about signal waveform associated with the designated wiring. Subsequently, another wiring is designated and then the same operations as described above are again made. Those processes are sequentially made for some or all of the wirings on the printed board, whereby a distribution in the calculated quantity of the electromagnetic interference over two-dimensional positions is obtained.
This two-dimensional distribution is visibly displayed for identifying the positions of the signal wirings emitting the electromagnetic waves causing the electromagnetic interference. This makes it easy to take an possible effective counter-measure to the electromagnetic interference.
The above described two conventional design support systems are adopted to suppress electromagnetic wave radiation from the signal wirings on the printed board. This electromagnetic wave radiation is so called to as xe2x80x9cnormal mode radiationxe2x80x9d or xe2x80x9cdifferential mode radiationxe2x80x9d. A xe2x80x9ccommon mode radiationxe2x80x9d is different from the xe2x80x9cnormal mode radiationxe2x80x9d or xe2x80x9cdifferential mode radiationxe2x80x9d. This xe2x80x9ccommon mode radiationxe2x80x9d also causes the electromagnetic interference from the printed board. In majority cases, the xe2x80x9ccommon mode radiationxe2x80x9d may be dominant over the xe2x80x9cnormal mode radiationxe2x80x9d or xe2x80x9cdifferential mode radiationxe2x80x9d.
A xe2x80x9cnormal mode currentxe2x80x9d causes the xe2x80x9cnormal mode radiationxe2x80x9d. A xe2x80x9ccommon mode currentxe2x80x9d causes the xe2x80x9ccommon mode radiationxe2x80x9d. The xe2x80x9cnormal mode currentxe2x80x9d and the xe2x80x9ccommon mode currentxe2x80x9d are high frequency currents which cause the electromagnetic interference. The xe2x80x9cnormal mode currentxe2x80x9d on the printed board means paired currents with the same quantity, which flow through a signal wiring and a ground plane respectively and in opposite directions to each other or in anti-parallel directions to each other. For example, the first one of the paired currents flows through the signal wiring in a first direction, and the second one of the paired currents flows through the ground plane in a second direction opposite to or anti-parallel to the first direction. The xe2x80x9cnormal mode currentxe2x80x9d may also be so called to as xe2x80x9cloop currentxe2x80x9d.
FIG. 3 is a schematic perspective view of explaining the normal mode current and the common mode current. The normal mode current is represented by a broken line. The common mode current is represented by a real line. First and second large scale integrated circuits LSI1 and LSI2 have a upper level than a ground plane. The first and second large scale integrated circuits LSI1 and LSI2 are inter-connected to each other through a horizontally extending signal wiring or interconnection which has the particular level upper than the ground plane. Each of the first and second large scale integrated circuits LSI1 and LSI2 is also connected to the ground plane through a vertically extending signal wiring or interconnection.
The normal mode current flows from the first large scale integrated circuit LSI1 through the horizontally extending signal wiring to the second large scale integrated circuit LSI2. Further, the normal mode current flows from the second large scale integrated circuit LSI2 through the vertically extending signal wiring to the ground plane. The normal mode current flows through the ground plane in a direction opposite to or anti-parallel to the direction along which the normal mode current flows through the horizontally extending signal wiring which inter-connects the first and second large scale integrated circuits LSI1 and [LSI2. The normal mode current further flows through the vertically extending signal wiring to the first large scale integrated circuit LSI1. As a result, the normal mode current flows so as to draw a loop in a vertical plane which is defined between the ground plane and the horizontally extending signal wiring different in level from the ground plane.
The common mode current flows in the ground plane. The common mode current is a differential current between a first part of the normal mode current flowing through the horizontally extending signal wiring and a second part of the normal mode current flowing through the ground plane, when the first anti second parts of the normal mode current are made different in quantity from each other by a certain cause. If a balance in current quantity is kept between the first and second parts of the normal mode current, then any differential current or common mode current does not flow. If the balance is lost by any cause, then the differential current or common mode current flows through the ground plane.
The normal mode current flows the looped or closed circuit. The common mode current flows through the two-dimensional space provided by the ground plane and may flow through a cable which is connected to the ground plane.
A distance between the horizontally extending signal wiring and the ground plane is so short that electromagnetic fields generated by the first and second parts of the normal mode current cancel each other, wherein the first and second parts of the normal mode current are opposite in phase to each other and have the same current quantity. If the current quantity of the normal mode current is small, a generated electromagnetic interference may be so small as being ignorable.
The common mode current, however, does not draw such a narrow loop that different parts of the common mode current cancel electromagnetic fields generated by the opposite parts. The common mode current is not limited in current path and is free to flow on two-dimensional space provided by the ground plane, for which reason the common mode current is likely to draw a wide loop which allows a certain or strong electromagnetic radiation.
It is relatively easy to have an accurate grasp of the normal mode current as flowing through the limited one-dimensional space provided by the signal wiring or interconnection. In contrast, the accurate cause for generating the common mode current has been unclear yet. The common mode current is extremely smaller in current quantity than the normal mode current. This makes it difficult to have an accurate grasp of a current path of the common mode current. For example, it was the conventional common sense that the normal mode radiation or the differential mode radiation may easily be suppressed by the design and layout of the product, but it is difficult to suppress the common mode radiation, for which reason the electromagnetic interference property of the product depends mainly on the common mode radiation.
Any effective design measure for suppressing the common mode current or the common mode radiation had not been developed before the present invention was invented by the present inventors.
In the above circumstances, the development of a novel free from the above problems is desirable.
Accordingly, it is an object of the present invention to provide a novel design support system for designing a printed board free from the above problems.
It is a further object of the present invention to provide a novel design support system for designing a printed board which is adopted to suppress a common mode radiation and a common mode current.
It is a still further object of the present invention to provide a novel method of designing a printed board free from the above problems.
It is yet a further object of the present invention to provide a novel method of designing a printed board which is adopted to suppress a common mode radiation and a common mode current.
It is further more object of the present invention to provide a novel computer program implemented for designing a printed board free from the above problems.
It is more over object of the present invention to provide a novel computer program implemented for designing a printed board which is adopted to suppress a common mode radiation and a common mode current.
The present invention provides a design support system including a basic functional block for designing a printed board including at least a ground layer; and a first additional functional block for finding at least one resonant frequency to the ground layer based on an information of a resonance-significant size of the ground layer.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.